Radio-occultation and in-situ measurements of plasma density in Halley’s comet plasma

First direct investigation of the Halley’s comet plasma mantle was performed during the VAGA-1 and VEGA-2 flybys in 1986 at the dayside with closed approaches of 8890 km and 8030 km, respectively. Onboard transmitters Radio-occultation experiment was performed with onboard transmitters in 32 cm and 5 cm ranges and ground receivers complex that recorded phase, frequency and power of radio waves [1]. Comparison of radio-physics effects of radio-waves propagation through Halley’s comet plasma envelope on March 6 and 9, 1986 with calibration measurements performed in time interval from February 14 till March 1986 allowed one to determine the profiles of electrons number densities. Direct measurements of ion ULF fluctuations, planetary heavy ion velocity, number density and mass were made along VEGA-1 and VEGA-2 trajectories by Faraday cups and planar electrostatic analyzers were performed by BD-3 sensor [2] of APVN instrument [3]. Results of these experiments and their comparison are presented in this talk.